Repo-relative indicator

[Bosco Rama]

Hey,

I have a strange question:  Is there a repo-relative indicator for
command-line paths similar to the bash '~' character?  Several times
recently I've been several levels deep in a different part of the tree
and have wanted to generate a 'hg diff' of a file in another part of the
tree.  So, I either have to use a bunch of '..'s or use an absolute
path to do this.  Short of setting my own '$repo' shell var and using
that do I have any other options within hg?

Nothing glaringly obvious shows up in the docs though there seem to be
some things that can be massaged to help.  Just thought I'd get a
definitive yay or nay from the collective before reinventing the wheel.

TIA,
Bosco.